Improve migrations to support migrating milestones/labels/issues/comments/pullrequests (#6290)

* add migrations

* fix package dependency

* fix lints

* implements migrations except pull requests

* add releases

* migrating releases

* fix bug

* fix lint

* fix migrate releases

* fix tests

* add rollback

* pull request migtations

* fix import

* fix go module vendor

* add tests for upload to gitea

* more migrate options

* fix swagger-check

* fix misspell

* add options on migration UI

* fix log error

* improve UI options on migrating

* add support for username password when migrating from github

* fix tests

* remove comments and fix migrate limitation

* improve error handles

* migrate API will also support migrate milestones/labels/issues/pulls/releases

* fix tests and remove unused codes

* add DownloaderFactory and docs about how to create a new Downloader

* fix misspell

* fix migration docs

* Add hints about migrate options on migration page

* fix tests

modules/auth/repo_form.go

@@ -51,10 +51,16 @@ type MigrateRepoForm struct {
 	// required: true
 	UID int64 `json:"uid" binding:"Required"`
 	// required: true
-	RepoName    string `json:"repo_name" binding:"Required;AlphaDashDot;MaxSize(100)"`
-	Mirror      bool   `json:"mirror"`
-	Private     bool   `json:"private"`
-	Description string `json:"description" binding:"MaxSize(255)"`
+	RepoName     string `json:"repo_name" binding:"Required;AlphaDashDot;MaxSize(100)"`
+	Mirror       bool   `json:"mirror"`
+	Private      bool   `json:"private"`
+	Description  string `json:"description" binding:"MaxSize(255)"`
+	Wiki         bool   `json:"wiki"`
+	Milestones   bool   `json:"milestones"`
+	Labels       bool   `json:"labels"`
+	Issues       bool   `json:"issues"`
+	PullRequests bool   `json:"pull_requests"`
+	Releases     bool   `json:"releases"`
 }
 
 // Validate validates the fields